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The stars and constellations drawn here represent what can be seen from urban areas, which is not the zodiac. The x-y display is as though you are lying down, feet to the south, and looking up at a cylindrical portion of the night sky. The grey earth plus atmospherics blockage zones are for 0 to 30 deg elevation above the geometric horizon formula. This software is not designed for zooming in.
The celestial zenith line is defined as positions that will pass directly overhead as you look up from your latitude. The horizontal solid line is for 40° mid-latitude US with the dashed lines indicating zenith for observers at 50° or 30° latitude. Grid line spacing is 30° with celestial equator de-emphasized to just a few dashes. It is important to learn the time sequence of what is in the evening sky as the year goes by, simulated here by dragging—or for drill, flick with grid off and see if you can state the time of year you end up on. Than click Grid back on to see if you got it right. Many other software packages like Stellarium are far more accurate but are not as simple to use for an initial learning tool. EZStars is meant to be a tutorial and memorization drill tool for people first learning stars, constellations and Messier objects. The names of sixteen stars, twenty constellations and locations of five sets of Messier objects can be toggled on and off with a keystroke. Key first letters shown, as "s" to toggle star names on and off or "a" for asterisms. For the five groups of Messier and other deep sky objects key a digit from 1 to 5—or to get the names as well, hold down Shift while keying the digit. In addition to learning locations for an initial subset of easier Messier objects, the objective is to learn where in the sky some of the more impressive Hubble-class imagery has come from and also some of the astrophysics. The table and notes on the left are an introduction, and you can compare the the difference in a Hubble-class image versus what you will see with a 4" telescope. Star wheels and tables do not agree on which Messier objects might be easier or more interesting to learn about. The ones used here are either from the 11" Sky & Telescope star wheel or are rated as easy by Ken Graun in his book ("The Next Step: Finding and Viewing Messier’s Objects"), plus some are just added for general interest. Messier1, the first group of six, is chosen to be fairly easy with Messier2 a little more challenging. Partial lists of harder to locate Messier objects are grouped as More and Deep, plus a Binocular Challenge. Indicated in Deep is a supernova remnant both below -40° and too dim for amateur telescopes to see. But it is interesting to know where SN1987a occurred (way below Orion) because it was the first time a core-collapse supernova was observed first by neutrino detection and then two to three hours later by visible light emissions.
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